Also, these balls do not magically make coaches better or less lazy. A lazy or bad coach is that way no matter what equipment they use.

I have seen these red, orange, green balls used for years now. Nothing has changed. The coaches who teach bad technique, take short cuts, rush kids into tournaments before they have proper fundamentals....they all still do that with the slower balls.

Good coaches can teach a kid with yellow balls from age 4 if they choose to with proper hand feeds. However, many do choose to use the lower bounce balls for training purposes, for the same reasons they used flat balls or poked holes in balls back in the day before low compression balls were on the market.

But this notion that the slower balls make coaches better is wrong. A lazy coach is not transformed by the equipment. Same with kids. Lazy or disinterested kids who do not want to learn tennis fundamentals are not changed by the balls. If the yellow balls are bouncing over their heads it is because they have not been taught the proper footwork or simply are not interested or too lazy to use the proper footwork.

Exactly. People don't understand (or see) the benefits of hitting yellow balls. A proper mix makes sense to me, but saying you can't hit a yellow ball until you can slice is freaking ridiculous.